Digitizing planimeter

Abstract

A planimeter includes a movable housing in which are mounted orthogonally aimed x- and y-position sensors. Each position sensor comprises a piezoelectric ultrasound transmitter and receiver for sending ultrasound to a reflector disposed on a drawing and sensing resultant echoes. Circuitry in the housing computes from the sensor outputs the housing's position for each of a sequence of locations on a drawing at which a user positions the housing, and from those it computes scaled distances between those positions as well as quantities that can be derived from those distances. The transmitter's and receiver's respective positions with respect to positioning crosshairs are such as to suppress the results of orientation errors. The planimeter's handle is angled at 45° to the directions in which the sensors are aimed so that it lends itself to both right- and left-handed operation.

1. A planimeter comprising:
 A) a housing; 
 B) a pair of distance sensors secured to the housing, each of which is associated with a different sensor region and includes:
 i) a radiation transmitter operable to send radiation into the sensor region associated with the distance sensor that includes that distance sensor; and 
 ii) a radiation receiver that is disposed in the housing and generates in response to echo radiation reflected from the sensor region associated with that distance sensor a sensor output dependent on that echo radiation; and 
 
 C) computation circuitry contained in the housing and so arranged as to:
 i) determine a respective two-dimensional position of the housing, for each of a sequence of locations of the housing, from the difference between times of radiation transmission and reception that occur while the housing is disposed at that location; 
 ii) store the sequence of two-dimensional positions thereby determined; 
 iii) compute at least one length from the difference between a pair of such two-dimensional positions in that sequence; and 
 iv) generate an output representative of a quantity that depends on at least one such length. 
 
 
   
   
     2. A planimeter as defined in  claim 1  further including a display, disposed on the housing, that provides a human-readable representation of the quantity that the output represents. 
   
   
     3. A planimeter as defined in  claim 1  wherein the circuitry accepts a scale input in accordance with which it scales outputs that it generates. 
   
   
     4. A planimeter as defined in  claim 1  wherein:
 A) the planimeter includes a positioning indicium adapted for alignment with a drawing feature; and 
 B) the determined two-dimensional positions are those of the positioning indicium. 
 
   
   
     5. A planimeter as defined in  claim 4  further including a transparent or translucent window in which the positioning indicium is provided. 
   
   
     6. A planimeter as defined in  claim 4  wherein each radiation sensor's radiation transmitter and receiver are so spaced from the positioning indicium that pivoting of the housing through small angles about the pivoting indicium from an orientation in which the sensor is aimed perpendicularly at an elongated reflector:
 A) results in an increase in the distance from the reflector to that radiation sensor's radiation transmitter if a decrease in the distance from the reflector to the radiation sensor's radiation receiver results from that pivoting; and 
 B) results in a decrease in the distance from the reflector to that radiation sensor's radiation transmitter if an increase in the distance from the reflector to the radiation sensor's radiation receiver results from that pivoting. 
 
   
   
     7. A planimeter as defined in  claim 6  wherein:
 A) each radiation sensor's radiation transmitter and receiver are so spaced from the positioning indicium that pivoting the housing through small angles about the positioning indicium from an orientation in which that sensor is aimed perpendicularly at an elongated reflector causes variations in the distances from that radiation sensor's radiation transmitter and receiver to the reflector; and 
 B) at least most of the resultant variation in the distance from the reflector to one of that radiation sensor's radiation transmitter and receiver is canceled by the resultant variation in the distance from the reflector to the other of that radiation sensor's radiation transmitter and receiver. 
 
   
   
     8. A planimeter as defined in  claim 1  wherein the radiation that the radiation transmitter sends and to which the radiation receiver responds is ultrasound. 
   
   
     9. A planimeter as defined in  claim 1  wherein the relative positions of the sensor regions with respect to the housing are fixed. 
   
   
     10. A planimeter as defined in  claim 1  wherein the angle between the directions in which the sensors are aimed differ by between 70° and 110°. 
   
   
     11. A planimeter as defined in  claim 10  wherein the angle between the directions in which the sensors are aimed differ by between 80° and 100°. 
   
   
     12. A planimeter as defined in  claim 1  wherein:
 A) the housing forms a handle portion; and 
 B) the direction of an axis of the handle portion is closer to that of the bisector of the angle between the sensor directions than it is to either of those directions themselves. 
 
   
   
     13. A planimeter as defined in  claim 12  wherein:
 A) the circuitry accepts a mode input that indicates whether the planimeter is to operate in a right-handed or left-handed mode; and 
 B) the two-dimensional position's determination depends on the mode thereby indicated. 
 
   
   
     14. A planimeter as defined in  claim 1  wherein:
 A) the planimeter further includes a display, disposed on the housing, that provides a human-readable representation of the quantity that the output represents; 
 B) the radiation that the radiation transmitter sends and to which the radiation receiver responds is ultrasound; and 
 C) the planimeter further includes user-operable keys, mounted on the housing, to which the circuitry responds. 
 
   
   
     15. A planimeter as defined in  claim 14  wherein:
 A) at least one said key is operable by a user to indicate that the housing is currently in one of the sequence of housing locations at which a respective two-dimensional position is to be determined; and 
 B) the planimeter generates a user-perceptible alert if its attempt to make the position determination was not successful. 
 
   
   
     16. A planimeter comprising:
 A) a housing that forms a handle portion; 
 B) a pair of distance sensors secured to the housing and so aimed that the direction of the handle portion's axis is farther from both of the directions in which the distance sensors are aimed than from the direction of the bisector of the angle between them, each of the distance sensors being associated with a different sensor region and including:
 i) a radiation transmitter operable to send radiation into the sensor region associated with the distance sensor that includes that distance sensor; and 
 ii) a radiation receiver that is disposed in the housing and generates in response to echo radiation reflected from the sensor region associated with that distance sensor a sensor output dependent on that echo radiation; and 
 
 C) computation circuitry so arranged as to:
 i) determine the housing's two-dimensional positions from the differences between times of radiation transmission and reception; 
 ii) compute a quantity from the positions thus determined; and 
 iii) generate an output representative of that quantity. 
 
 
   
   
     17. A planimeter as defined in  claim 16  wherein:
 A) the circuitry accepts a mode input that indicates whether the planimeter is to operate in a right-handed or left-handed mode; and 
 B) the two-dimensional position's determination depends on the mode thereby indicated. 
 
   
   
     18. A planimeter comprising:
 A) a housing that forms a positioning indicium adapted for alignment with a drawing feature; 
 B) a pair of distance sensors secured to the housing and so arranged that
 i) each of the distance sensors is associated with a different sensor region; 
 ii) each distance sensor includes:
 a) a radiation transmitter operable to send radiation into the sensor region associated with the distance sensor that includes that distance sensor; and 
 b) a radiation receiver that is disposed in the housing and generates in response to echo radiation reflected from the sensor region associated with that distance sensor a sensor output dependent on that echo radiation; and 
 
 iii) each radiation sensor's radiation transmitter and receiver are so spaced from the positioning indicium that pivoting of the housing through small angles about the pivoting indicium from an orientation in which the sensor is aimed perpendicularly at an elongated reflector:
 a) results in an increase in the distance from the reflector to that radiation sensor's radiation transmitter if a decrease in the distance from the reflector to the radiation sensor's radiation receiver results from that pivoting; and 
 b) results in a decrease in the distance from the reflector to that radiation sensor's radiation transmitter if an increase in the distance from the reflector to the radiation sensor's radiation receiver results from that pivoting; and 
 
 
 C) computation circuitry so arranged as to:
 i) determine the positioning indicium's two-dimensional positions from the differences between times of radiation transmission and reception; 
 ii) compute a quantity from the positions thus determined; and 
 iii) generate an output representative of that quantity. 
 
 
   
   
     19. A planimeter as defined in  claim 18  wherein:
 A) each radiation sensor's radiation transmitter and receiver are so spaced from the positioning indicium that pivoting the housing through small angles about the positioning indicium from an orientation in which that sensor is aimed perpendicularly at an elongated reflector causes variations in the distances from that radiation sensor's radiation transmitter and receiver to the reflector; and 
 B) at least most of the resultant variation in the distance from the reflector to one of that radiation sensor's radiation transmitter and receiver is canceled by the resultant variation in the distance from the reflector to the other of that radiation sensor's radiation transmitter and receiver. 
 
   
   
     20. A planimeter as defined in  claim 18  further including a transparent or translucent window in which the positioning indicium is provided. 
   
   
     21. A planimeter as defined in  claim 18  wherein both of the position sensors are aimed toward the positioning indicium.